Drugs are commonly administered orally by absorption through a patient's digestive tract. This method of drug administration involves systemic delivery of high doses of a drug which results in only a small percentage of the drug reaching a target area. Because of the high dosage, toxic side effects are often involved. In order, to address these problems alternative forms of drug delivery are being used for an increasing number of applications. The alternative forms of drug delivery typically involve: (i) inhalation, and (ii) trans skin or transdermal transport which is technically known as transdermal drug delivery.
Drug delivery via inhalation can involve an aerosol form of a drug. Aerosol forms of a drug are usually provided by atomization of a liquid solution form of the drug to form aerosol, immediately prior to drug delivery. Atomization is typically most efficiently effected by nebulization of a liquid, usually but not exclusively, with an ultrasonic nebulizer.
Ultrasonic nebulizers typically include an ultrasonic transducer which is positioned below a liquid filled container. For example, in more efficient nebulizers the ultrasonic transducer is designed to focus ultrasonic radiation to a specific point within the container. The focussed radiation results in formation of an upwardly projecting fountain of liquid and the formation of aerosol droplets at the fountain. Ultrasonic nebulizers operate efficiently when the liquid surface passes through the focal point of the ultrasonic transducer. However, they operate poorly or not at all if the liquid surface is above or below the ultrasonic transducer focal point. Conversion of liquid to aerosol causes the liquid surface to lower which in turn adversely affects a nebulizer's efficiency.
Transdermal drug delivery can involve passive diffusion and active transport. Passive diffusion of a drug through the skin is the diffusion that occurs naturally when small-molecule drugs are applied to the skin in sufficient concentration and for a sufficient period of time to enable natural diffusion through the skin. However, passive diffusion is slow and furthermore, because of the skin's natural barriers to passage of externally applied substances, passive diffusion is not suitable for most drugs. Active transdermal drug delivery techniques include sonophoresis, iontophoresis, electroporation and magnetophoresis. Sonophoresis involves the application of ultrasound, iontophoresis and electroporation involve the application of an electric field and magnetophoresis involves the application of a magnetic field.
U.S. Pat. No. 5,741,317 discloses an apparatus which includes a therapy and drug treatment tub for submersion of a treatment area of a patient in a medicated solution. The tub includes acoustic transducers and rows of electrodes and coils for delivery of respective ultrasonic, electric and magnetic radiation to the patient. The radiation facilitates active transdermal drug delivery involving phonophoretic, iontophoretic and electromagnetophoretic transport mechanisms. However, the apparatus is very large and expensive and cannot readily be used for transdermal drug delivery to a specific region of a patient.
U.S. Pat. No. 5,983,134 discloses a flexible cuff connected to a liquid drug reservoir. The cuff is designed for attachment to a patient by wrapping around part of the patient's body to form an attached sleeve. Referring to FIG. 1 of U.S. Pat. No. 5,983,134, the attached sleeve can be elongate and encircle most of a patient's leg, or squat and encircles a patient's neck. The cuff is designed to transmit electric and magnetic fields to assist transdermal delivery of drugs provided at an internal cylindrical surface of the attached sleeve. While the cuff of U.S. Pat. No. 5,983,134 is suitable for transdermal drug delivery to a specific part of a patient's body, it is cumbersome to use and is only suitable for delivery of a drug to a circumferential segment of a patient's limb, torso or neck.
U.S. Pat. No. 5,464,386 discloses a transdermal drug delivery applicator which is designed to supply a fluid medium carrying drug loaded vesicles to a patient's skin via a curved head assembly. The applicator generates a pulsed electrical field to facilitate active transdermal transport mechanisms of electroporation and iontophoresis. The applicator is capable of providing active transdermal drug delivery to a specific part of a patient's body. However, the applicator is only able to provide active transdermal drug delivery involving electric radiation.